Estimation of Divergence Times and Reconstruction of Ancestral Morphological Characters of the Genus Mimosa (Leguminosae, Caesalpinioideae)

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Abstract— The subfamily Caesalpiniodeae has been the subject of several recent taxonomic delimitations, placing Mimosa in what is recognized as the “Mimosa clade.” Specifically, in recent decades several phylogenetic studies have been conducted with regard to the genus, but the estimation of the divergence times of some previously unanalyzed species was unknown and the reconstruction of ancestral morphological states to date has been limited to the mapping of characters on a phylogenetic tree. The aim of the present study was to perform a phylogeny based on the trnD2-trnT and rpS16 cpDNA markers as well as 19 morphological characters. We use these results to estimate the divergence times for Mimosa including some species not previously analyzed. In addition, we reconstructed the ancestral states using a chronogram for eight morphological characters: 1) leaf nectaries, 2) brachyblasts, 3) stamens, 4) staminodes, 5) type of flower, 6) type of inflorescence, 7) fruit dehiscence, and 8) fruit shape. Our results suggest that Mimosa originated in the Americas during the late Oligocene and that the genus shows recent diversification and numerous lineages in Mexico and South America, especially after the Pliocene and up to the present. The reconstruction of ancestral states reveals the tendency of the most recently divergent species toward reduction in flower parts and in some cases the preservation of plesiomorphic morphological character states.